The present invention pertains to the manufacture of corrugated paper board, and more specifically, to the application of a liquid bonding agent to the web of corrugated paper board prior to combining the web to a liner in a single facer machine or a double facer glue machine.
In a conventional single facer machine, a web of medium is corrugated as it passes between a pair of meshed fluted rolls. The corrugated web of medium is thereafter brought in contact with the surface of an adhesive applicator roll. The adhesive applicator roll usually has a lower surface speed than that of the corrugated medium and as a result thereof adhesive is transferred to the crests by a wiping action. The thusly processed medium is then bonded to a web of liner board by pressure from a pressure roll.
The usual practice has been to utilize an adhesive applicator roll having a roughened surface to retain a thin film of adhesive. The thickness of the film was governed by the gap between the adhesive applicator roll and a doctor roll or wiper blade. The amount of adhesive applied was also affected by changing the speed of the applicator roll relative to machine speed. This was known as the taper speed adhesive roll drive. Its principal objection was the application of a greater amount of adhesive at slow than at high speeds, thereby wasting adhesive at slow speeds. Many attempts were made to overcome this disadvantage. One of the principal alternatives was the application of adhesive in stripes on the liner in a pattern corresponding to the flute pitch. Representative of prior art patents on that alternative are U.S. Pat. Nos. 1,135,509; 1,609,318; 2,051,319; and 2,531,036.
Other attempts were directed to an adhesive applicator roll having a gravure or cell-embossed surface. The cells were intended to hold a predetermined quantity of adhesive so that only a uniform amount of adhesive would be applied to the flute crests. This type of roll was generally rotated at the same surface speed as the corrugated medium so that only the adhesive from a single row of cells would contact the flute crests.
While the procedures outlined above have been followed for many years, there are still disadvantages and objections. In addition to the wastage of adhesive by the application of a surplusage which wastes heat for drying and gelling, there is no way to apply a predetermined amount of adhesive and at the same time vary the amount applied to suit the characteristic of the paperboard being produced. The adhesives in general use an emulsion of starch, water and various alkalis to modify the gellatinization temperature. Some adhesives employ a gelled starch carrier containing various amounts of raw starch. Starch is an organic chemical and exhibits different characteristics depending upon the refining method whether made from corn, potato, or tapioca and the amount of associated water.
Corrugating mediums vary in their degree of hydroscopicity. Liners on the other hand are comparatively dense and do not readily absorb liquid adhesive. These variables have provided a need in the industry for means to vary the amount of adhesive applied to the flute tips while applying only a predetermined amount. There is also a need for the solution of this problem in the specific environment of corrugators which use cold-setting adhesives or bonding agents whereby the corrugator will be energy saving.